1. Field of the Invention
This invention relates to disk drive suspensions and, more particularly, to components for disk drive suspensions. In disk drive suspensions, the load beam that carries the slider adjacent the disk is supported in cantilevered relation from an actuator arm that is shifted to correspondingly move the slider by way of the load beam. The load beam is attached to a mount plate that comprises a base and a boss and the mount plate is then attached to the actuator arm, frequently by staking the mounting plate boss to an opening in the actuator arm.
The invention replaces the usual staking method of attachment with split ring techniques that offers numerous advantages.
2. Related Art
Patents on mounting load beams to actuators include U.S. Pat. Nos. 4,829,395, 5,172,286, and 5,187,626. In these and similar devices the mounting plate annular boss is deliberately made undersized relative to the mating circular opening in the actuator arm but of a malleable metal so that the boss can be expanded to a friction fit with the surrounding arm opening. The arm may be one or a series of arms formed from a machined casting (i.e. an actuator arm or an E-block) to which one or more head gimbal assemblies (HGAs) are to be attached by staking or swaging. The resulting assembly is a head stack assembly (HSA). As shown in U.S. Pat. No. 4,829,395, a ball, or two, each progressively oversized relative to the inside diameter of the boss is passed through each boss within a surrounding arm opening aligned in a stack and by staking or swaging the boss outward make an interference fit between the HGA boss ODs and the ID of the hole in the actuator. With reference to FIG. 6A PRIOR ART the actuator arm 1 has a circular opening 2 of a predetermined diameter. Mount plate 3 has an annular boss 4 that is smaller in diameter than opening 2 and easily fits into the opening. Boss 4 has a bore 5 of a predetermined ID selected, as is the metal used, to permit deformation of the boss wall 6 into the surrounding opening 2. Ball 7 has diameter smaller than the opening 2 but larger than the ID of the boss bore 5. When forced through the bore 5 the ball 7 forces the boss wall radially into the inner wall 8 of the opening 2 to stake the mount plate 3 to the arm 1. See FIG. 6B, PRIOR ART.
The known method of staking the HGAs inevitably results in deformation of the mount plate. The deformation results in variations in the gram load (preload) applied by the suspension to the slider both as a function of staking direction or orientation (up facing as opposed to down facing) and also randomly due to part dimensional variation. Attempts to improve this usually trade off cost, by making the parts more precise or other performance parameters. For example, the gram load change can be reduced (improved) by making a less rugged attachment, trading torque resistance for gram change.
The industry trend is, however, toward allowing ever smaller tolerances on gram load variation while simultaneously seeking ever lower cost of each piece part and assembly. Variation in gram load is to be minimized as a cost-increasing factor to the disk drive. A common practice to overcome the variation in gram load is to make an adjustment to the stack by "tweaking" the suspension after the staking step takes place. This involves extra labor and thus cost and impacts yields of the assemblies as well again increasing costs.
When an HGA has the gram load changed from the original value, the target optimization of the suspension is lost. Such optimization is a key step in the suspension fabrication process whereby the mandrel that forms the preload on the suspension is adjusted for radius and location in such a way that the harmful resonances of the suspension are minimized. Typically, this part of the fabrication set-up may take several days to accomplish, and once done is kept until the set up is broken done to make something else on that assembly line. When the suspension is adjusted from the original value in gram load without the requisite precision, including the evaluation of the resonance effects, the optimization is lost and the suspension may induce resonances in the HAS or the disk drive. In the worst case, this could result in an inoperable drive assembly that would fail before it left the disk drive manufacturer.